Be careful who you let in your home especially if you live in a multi unit building. Recently in very nice neighborhoods in San Francisco, convicted violent felons have been getting into buildings through the front door. It appears in some cases someone has just “buzzed” them in without seeing who they were. Another reason for people to have visual door monitors. (gee maybe I should be plugging a company:)
Also, verify someone who purports to be a utility person or uniformed vendor.
Taking that extra step to see who is there could save your life or the very least, your possessions.